When drugs of abuse are smoked, volatile components and pyrolysis material escape into the atmosphere. Depending on the local environment, bystanders may be exposed to the drug by passive inhalation of the contaminated air. Artificial methods have been developed to smoke drugs of abuse in a controlled environment and to measure drug air levels. These methods are then applied to the design of human clinical studies to assess the hazards of environmental exposure to drugs. Initially, free-base cocaine "crack" and methamphetamine "ice" will be evaluated. Unknowing drug exposure could be dangerous to unsuspecting bystanders, particularly to small children. These studies will establish limits of exposure to volatile components of drugs under controlled conditions.